​Pilot study on the incidence of algal toxins (ASP, DSP and PSP toxins) in Scottish Brown Crab (Cancer pagurus)

Summary

Integrin Advanced Biosystems Ltd
Vincent, D ; Ward, C; Mckenzie, J; Latif, Z; Williams, M

The Brown Crab, Cancer pagurus is a significant fishery in Scotland, worth approximately £10M per annum. Consumption of brown crab in Norway recently resulted in a mass poisoning through the presence of diarrhetic shellfish toxins in the crab tissue that originated from marine algae toxins. Algal biotoxins including DSP are regularly detected in bivalve molluscs harvested in Scotland, but very little is known about their prevalence in crabs fished in Scottish waters. The poisoning incident in Norway prompted the Food Standards Agency Scotland (FSAS) to commission a pilot study to investigate the potential for crabs from Scottish waters to act as a vector for algal biotoxins.

The study consisted of three main components. Firstly, the crab industry in Scotland was mapped, primarily through analyses of landing data. It was determined that the nominal fishing season coincides with the biotoxin season – both being at their height in the British summer and autumn months. Over 95% of crab landings occur in only 12 ports in Scotland and these are predominantly in the West and far North-East of Scotland (including Orkney). The areas where crabs are fished also tend to coincide with areas of high biotoxin production.

Secondly, to ascertain the presence of toxin-contaminated crabs in the wild, field samples were taken during 2005 and 2006. During 2005, targeted sampling of crabs was conducted in areas that had a history of toxic events and further reactive sampling was undertaken from areas where the FSAS monitoring programme detected toxins in bivalves. The results showed that both PSP and ASP toxins were commonly detected in wild crabs (crabs with detectable PSP levels: 83% and detectable ASP levels: 35%). Within an individual sampling area, crabs sampled at the same time were highly variable with regard to the concentrations of toxins present. This was particularly true of ASP toxins. Few crabs (<5%) were found over the regulatory limit set for bivalves for either ASP or PSP toxins, however one crab was found to contain six times the regulatory limit for ASP and another over twice the regulatory limit for PSP. Despite the occurrence of a small number of toxic events during 2005 involving DSP in bivalve molluscs, DSP toxins were not detected in any of the crabs sampled during 2005.

During 2006, crabs were randomly sourced from three separate, but important, fishing areas and tested for ASP and PSP toxins. In addition, crabs were also sampled from one area where DSP toxins were detected in bivalve molluscs through the FSAS biotoxin monitoring programme. The results for 2006 were similar to 2005, in that ASP and PSP toxins were regularly detected in the crabs. Again, both ASP and PSP toxins tended to be detected at low concentrations, although high levels were occasionally detected in individual crabs. DSP toxins were also detected in crabs sampled during 2006, although at low levels.

Thirdly, laboratory feeding studies were conducted to investigate uptake of ASP and DSP toxins by crabs. These experiments were also intended to provide toxic material for the validation of testing methods used throughout the study. Although limited, these experiments demonstrated accumulation of both ASP and DSP toxins in crabs fed exclusively on toxic shellfish. One feeding experiment also provided some evidence of reduced feeding if the food source contained particularly high levels of ASP toxins.

The results of this pilot study suggested that Scottish Brown crabs could potentially be a vector for ASP, DSP and PSP when conditions are suitable. Suggestions for further studies and possible actions to help prevent the risk of contaminated crabs being placed on the market are also provided in this report.

Project Code: S14017